The present invention relates to a transmission apparatus and a transmission method for transmitting optical signals subject to multiple-wavelength.
In order to reduce system costs while increasing the capacity of communications, a multiple-wavelength optical transmission technique for communicating a plurality of signal light rays of different wavelengths by tying them up into a single optical fiber has generally been applied to an optical communication system. In an actual system, a multiple-wavelength functional device, that is, a wavelength multiplexer device is installed which is constituted by a light ray insert unit adapted to bundle a plurality of signal light rays of different wavelengths into a single optical fiber, a light ray split unit adapted to split, wavelength by wavelength, the bundled plural signal light rays, and an optical fiber amplifier unit adapted to compensate an optical signal for a loss generated in an optical fiber representing a transmission path between two remotely distant locations. Provided for the wavelength multiplexer device is a transponder which converts a light signal into that having a wavelength suitable for multiple-wavelength. By using the wavelength multiplexing device and an interface device in combination, inexpensive communication can be offered over a long distance.
Reference is now made to FIG. 1 illustrating a general network configuration using a multiple-wavelength transmission system. Structurally, the network includes an access quarter 1-4 for offering FTTH (Fiber To The Home) service to subscribers in a unit of areas by using an OLT (Optical Line Terminal) unit 1-2 and an ONU (Optical Network Unit) 1-3, an edge quarter 1-6 for concentrating communications from subscribers in area units into a group of areas by using a switch 1-5 of a plurality of L2's (Layers 2), a metro quarter 1-7 for concentrating the communications concentrated by the L2 (Layer 2) switch into a unit of towns and cities, and a core quarter 1-8 for efficiently transmitting a large capacity of communications concentrated in a unit of towns and cities over a long distance between metropolitans. In the present network, an ODAM (Optical Add Drop Multiplexer) device as designated at reference numeral 1-1 represents an optical transmission system used for concentrating into a single location the communications scattered in a relatively wide range.
Turning to FIG. 2, the OADM device 1-1 is generally constructed as exemplified therein. In FIG. 2, two OADM devices 1-1 are so configured as to oppose to each other with intervention of two transmission paths 2-1. The OADM device 1-1 includes a wavelength multiplexer unit 2-5 adapted either to take out a desired signal from a plurality of light signals subject to multiple-wavelength or to pile the desired signal up again into a group of plural signals by causing the desired signal to undergo multiple-wavelength, a transponder unit 2-3 adapted to either suitably convert a signal split from the wavelength multiplexer unit 2-5 by discriminating it from a subscriber signal accommodated in the OADM device 1-1 or to suitably convert the subscriber signal and cause it to undergo multiple-wavelength by means of a splitter/inserter, and a supervisory control unit 2-4 adapted to perform supervisory control of the wavelength multiplexer unit 2-5 and transponder unit 2-3.
A supervisory control light controlling unit 2-2 causes a signal light ray 2-7 outputted from the transponder unit 2-3 and a supervisory control tight ray 2-6 outputted from a supervisory control light processing unit 2-4-1 under the control of the supervisory control unit 2-4 to undergo multiple-wavelength and transmits them to the transmission path 2-1. Also, the supervisory control light controlling unit 2-2 causes the signal light ray 2-7 subject to multiple-wavelength and received from the transmission path 2-1 and the supervisory light ray 2-6 from the supervisory control light processing unit 2-4-1 to undergo wavelength splitting, respectively, and the individual split light rays are inputted to the transponder unit 2-3 and the supervisory control unit 2-4, respectively.
In the OADM device 1-1 shown in FIG. 2, the signal light ray 2-7 propagates through a path indicated at dotted line and the supervisory control light ray 2-6 propagates from the supervisory control light processing unit 2-4-1 through a path as indicated at solid line. More particularly, the light ray from the supervisory control light processing unit 2-4-1 is split by means of the supervisory control light controlling unit 2-2 in the opposing OADM device 1-1 and inputted to the supervisory control light processing unit 2-4-1 in the opposing OADM device 1-1. The signal light ray 2-7 passes through the supervisory control light controlling unit 2-2 and is then inputted to the wavelength multiplexer unit 2-5.
Turning to FIG. 3, an explanation will diagrammatically be given to a multiple-wavelength light ray having a signal wavelength group 3-2 subject to multiple-wavelength and a supervisory control signal 3-1. In a general OADM device 1-1, there exist, as described in JP-A-2003-046456, for example, the signal group of plural signals subject to multiple-wavelength carrying actual communication data and the supervisory control signal 3-1 adapted to materialize communication of signals used for executing mutual control and supervisory of the OADM devices 1-1 located remotely. In FIG. 3, the signal wavelength group 3-2 of 32 signals subject to multiple-wavelength and the single supervisory control signal 3-1 arranged on the side of short waves are illustrated but when the supervisory control signal 3-1 arranged on the side of long waves or when a plurality of supervisory control signals 3-1 are arranged, a number other than 32 of signal waves will sometimes be subjected to multiple-wavelength.
In the general OADM device 1-1, the function to take out a desired signal from a plurality of optical signals or execute multiple-wavelength of the desired signal and to pile it up into the group of plural signals is executed in the wavelength multiplexer unit 2-5. For communication of the supervisory control signal between the remotely located OADM devices 1-1, only the supervisory control signal is split from the light rays subject to multiple-wavelength by means of the supervisory control light controlling unit 2-2 arranged in the input port from the transmission path 2-1, for example, and is then inserted or merged to the signal wavelength by means of the supervisory control light controlling unit 2-2 arranged in the output to port of the transmission path 2-1.
Reference is now made to FIG. 4 to indicate how an external device 4-1 such as a router is connected to the transponder unit 2-3 and the wavelength multiplexer unit 2-5. The transponder unit 2-3 is comprised of a multiple-wavelength side interface section 2-3-1 and an external device side interface section 2-3-4. The multiple-wavelength side interface section has a transmitter 2-3-2 and a receiver 2-3-3. The transmitter 2-3-2 converts an optical signal to that having a wavelength suitable for multiple-wavelength and sends it to the wavelength multiplexer unit 2-5 and the receiver 2-3-3 receives an optical signal sent from the wavelength multiplexer unit 2-5. Similarly, the external device side interface section 2-3-4 has a transmitter 2-3-6 and a receiver 2-3-5 to thereby receive an optical signal from the external device 4-1 or transmit an optical signal thereto. Similarly, the external device 4-1 has a transmitter 4-2 for transmission to the transponder unit 2-3 and a receiver 4-3 for reception from the transponder unit 2-3. Since the signal transmitted from the external device 4-1 does not always have a wavelength suitable for multiple-wavelength, an optical signal transmitted from the transmitter 4-2 of external device 4-1 cannot be inputted to the wavelength multiplexer unit 2-5 while keeping its wavelength intact.
It is necessary for the OADM device 1-1 of the general construction as above to add a transponder unit 2-3 each time it connects to the external device 4-1. As a result, in case a plurality of external devices 4-1 are connected, the number of transponder units 2-3 to be installed must be increased and consequently, the cost of the system rises.
To cope with this problem, the wavelength of a signal outputted from the transmitter 4-2 of external device 4-1 is made in advance suitable for multiple-wavelength to permit connection to the wavelength multiplexer unit 2-5 without resort to the transponder unit 2-3, thus reducing the system cost.
The transponder unit 2-3, however, does not function merely to convert the wavelength of optical signal into that suitable for multiple-wavelength but is used to separate and identify a location where a fault occurs inside the network using the OADM device 1-1 and therefore, the aforementioned expedient needs a construction for separating a fault and identifying a fault interval during occurrence of the fault, eventually raising a problem that the running cost increases and as a result, the total cost is raised.
In order to facilitate handling the fault generation in the OADM device without the transponder unit 2-3 as described above, two countermeasures of 1) intensifying the function of supervisory the external device 4-1 has and 2) intensifying the function of supervisory the OADM device 1-1 has are conceivable.
Of them, in connection with the method for intensifying the supervisory function provided for the external device 4-1 as in 1), a method of intensifying the function to supervise a physical layer such as for optical input/output supervisory provided for the external device 4-1 and a method of intensifying the function to supervise a data link layer and a network layer such as Inthernet (registered trade mark) OAM, MPLS OAM are conceivable. Any of the supervisory functions, however, does not supervise the inside of OADM device but gives the end-to-end supervisory function executed externally of the OADM device. Therefore, when a fault occurs inside the network using the OADM device, specified information cannot be obtained as to where the fault occurs inside the OADM device and how the fault is to be dealt with. In other words, so long as the mere end-to-end supervisory from the outside is executed, the fault developing inside the OADM device cannot be separated specifically.
Further, solving the present problem by the provision of the new function for the external device 4-1 means that the external device 4-1 having already been introduced into the network cannot be utilized because it lacks the new function.
In connection with the method of intensifying the supervisory function the OADM device 1-1 has as mentioned in 2) above, the presence/absence of a fault can be confirmed in respect of each optical signal by providing the function to supervise individual optical signals undergoing multiple-wavelength and accordingly, the supervisory function can be intensified. But the supervisory function as above needs to be provided by the number of accommodated multiple-wavelengths, making the construction complicated and raising the cost of the OADM device per se. Further, by providing the function to analyze optical characteristics as in the case of an optical spectrum analyzer, supervisory of each optical signal can be intensified but the construction becomes complicated and besides, because of very high expensiveness of the optical spectrum analyzer, the cost of the OADM device 1-1 per se still arises.
As will be seen from the foregoing, in the OADM device without the transponder unit 2-3, separation of a fault developing in the network using the OADM device 1-1 must be realized by avoiding complexity and expensiveness.